1. Field of this Invention
This invention relates generally to a target structure for an image pickup tube, and more particularly to such a target structure that employs, as a photo-conductive material, either amorphous selenium or antimony trisulfide.
2. Description of the Prior Art
There have been proposed many types of target structures for use in a television pickup tube. For example, antimony trisulfide is well-known as a photo-conductive material in a target structure. The target structure is usually formed of a face-plate made of glass a, transparent electrode made of tin-oxide usually called Nesa (trade mark), and a photo-conductive layer of antimony trisulfide. A pickup tube which employs the target structure above described is widely used in this field but it is known that the dark current characteristics and residual image characteristics thereof are less than desirable. Further, dust undesirably attaches to th surface of the tin-oxide during fabrication and deteriorates the output video signals from the image pickup tube. Another type of a prior art target structure employs principally amorphous selenium as its photo-conductive material. The improvement of residual image characteristics is as expected by using this photo-conductive material, but the shortened life time of an image pickup tube based on the low crystallizing temperature of amorphous selenium has prevented its practical use.